As a flexible hose for connecting to, e.g., an electric cleaner, there has been known a bellows hose whose hose wall is constituted of spiral concaves and convexes throughout its length. However, when the hose is attached to an electric cleaner or the like and the cleaner is operated, such spiral concaves and convexes formed inside the hose result in a great pressure loss and high suction resistance, and deteriorate the suction performance of the hose.
Japanese Patent Application Laid-Open No. 265237/1995 (JP-A-7-265237) discloses a cleaner hose wherein a reinforcing wire is spirally wound. In this reference, at least one end of the hose is formed such that the turns of the spirally wound reinforcement are tightly adjoining or adjacent each other at a steep angle with the hose wall between the turns inwardly folded (an expandable and contractible zone or region of the required length), and other part of the hose is formed such that, in its normal state with the hose wall stretched, the turns of the spirally wound reinforcement are apart from each other in the axial direction of the hose at a gentle angle. Since the expansion and contraction zone or region is expansible, contractible and bendable, such cleaner hose is easier to handle and has a reduced ventilation resistance in the middle region of the hose. When the hose is in a state of contraction, however, the ventilation resistance can not be reduced to a great extent due to the inwardly extending folded hose wall between the turns of the reinforcing wire.
Japanese Patent Publication No. 12040/1968 (JP-B-43-12040) discloses the method for producing a compressible hose, which comprises folding the hose wall inwardly to form a fold between the adjoining turns of the wire reinforcement, thrusting a core mold into the hose to make the folds incline in the same direction, and bending or curving the wall of the folds. When the direction of the inclination and the direction of the flow of a fluid are the same, it is possible to reduce the flow resistance of a hose obtained by this method. However, when a fluid flows from the direction opposite to the direction of the inclination of the folds, flow resistance increases significantly. As a result, electricity is highly consumed, hence economically disadvantageous. Furthermore, depending on the structure of a hose, the folds inside the hose sometimes can not be inclined, and applications of the hose are limited.
In particular, when a hard steel wire and a copper wire are disposed in parallel and used as a spiral reinforcement, a spiral groove inside the hose is widened with contraction of the hose, and the widened groove renders it difficult to reduce the ventilation resistance of the hose which is in a state of contraction.